This invention relates to speed sensing devices and is particularly concerned with a novel speed sensor especially useful for an automotive vehicle.
Speedometer systems currently in use in automotive vehicles are generally mechanical type systems wherein speed information is generated by a speedometer gear in the transmission. The speedometer gear is operatively coupled with the vehicle speedometer via a speedometer cable assembly. In anti-skid braking systems and speed control systems utilized in automotive vehicles, speed information is generated electrically via various types of electromagnetic pick-up devices. ;p The present invention is concerned with a novel electromagnetic pick-up device which itself has no moving parts but rather is utilized in conjunction with the existing transmission to provide an electrical speed signal representative of vehicle speed. A pick-up device embodying principles of the present invention results in simpler contruction, convenient mounting on the vehicle, ruggedness in use and reliability, all while generating accurate speed information. The invention arises in part through the recognition that the aluminum casing of a transmission has no influence on a magnetic circuit passing through the casing and through the recognition of the availability of a toothed ferromagnetic gear which rotates adjacent the casing and is directly operatively coupled via the driveshaft and axle with the rear wheels of the vehicle.
The foregoing features, advantages and benefits of the present invention will be seen in the ensuing description and claims which are to be considered in conjunction with the accompanying drawing wherein there is illustrated a presently preferred embodiment of the invention according to the best mode presently contemplated in carrying out the invention.